1. Field of the Invention
The present invention relates to a valve for metering dry bulk powdered materials, such as for example cement. The primarily purpose of this valve is to proportionally meter bulk material for a blending or mixing operation. This design has an approximately linear characteristic wherein equal displacements of the valve sleeve will obtain approximately equal increases in valve opening area. This arrangement makes it well suited to automatic control of bulk materials.
Specifically, the present invention is an improved metering valve that addresses a variety of problems related to current metering valves, i.e. the problems of dry powdered material accumulating between the valve sleeve and the valve housing thus making the valve hard to turn, excessive wear on the valve caused by the abrasive action of the dry powdered material, incomplete sealing the valve when the valve is closed, and dry powdered material plugging off the vacuum breakers provided on the valve. In addition “dirty” cement may contain small rocks and other foreign material that may interfere with the normal operation of the valve. The foreign material may lodge in between the valve sleeve and body thus causing the valve not to turn or causing damage to the valve mating surfaces.
2. Description of the Related Art
Current metering valves employed to meter dry bulk powdered material, such as cement, present a variety of problems. First, current metering valves have a problem with dry powdered material accumulating between the valve sleeve and the valve housing. Because both the valve sleeve and the valve housing are circular in shape and the clearance between the valve sleeve and valve housing on current metering valves is uniform around the entire circumference of the valve sleeve, the dry powdered material tends to pack into the gap separating the valve sleeve and housing and forms a hardened layer between the two valve members. This hardened layer causes wear of the valve and can ultimately cause the valve sleeve to bind or freeze up within the housing. The valve must then be taken out of service and disassembled so that the hardened layer can be chipped off of the valve. Removing the valve from service for this type of maintenance is time consuming, labor intensive, and costly.
A second problem with current metering valves is that the leading edge of the sleeve opening provided in the valve sleeve is the point at which the greatest wear due to abrasion by the dry powdered material occurs. Excessive wear on the valve caused by the abrasive action of the dry powdered material allows more of the dry powdered material to enter the gap between the valve sleeve and the housing, thus acerbating the previously described problem of dry powdered material forming a hardened layer in the gap.
Also, with the leading edge of the sleeve opening worn by the abrasive action of the dry powdered material, the valve does not seal tightly when the valve is closed.
A final problem with current metering valves in that dry powdered material sometimes enters the mouths of the vacuum breakers provided in the valves and plugs off the openings to the vacuum breakers. If dry powder becomes plugged within the vacuum breakers, this may allow bulk material to be discharged externally, thus causing an environmental problem for the operator. He may not be able to see due to dust, and the dust is unhealthy to breathe. Current metering valves have the mouths of the vacuum breakers open to the housing of the valves, thus allowing dry powered material to fly into the mouths and come into contact with the moisture. The moistened powdered material will then set up and over time will completely plug the openings to the vacuum breakers, making the vacuum breakers inoperative.
The present invention addresses these problems by providing a metering valve with greater clearance between the valve sleeve and housing in the areas not adjacent to the metering edges of the housing. With greater clearance between the valve sleeve and housing except at the sealing surface or lip, the problem of creating an unwanted hardened layer or interference with foreign particles in the gap separating these valve elements is either eliminated or greatly improved.
The present invention also is provided with an eccentric intermediate sleeve that serves to align the valve sleeve relative to the housing. By rotating the intermediate sleeve slightly, this rotational motion of the intermediate sleeve translates into a back-and-forth motion of the valve sleeve, thus moving the valve sleeve either nearer or further from the front side of the valve body, i.e. the side of the valve body through which the dry powdered material enters the valve.
The ability to move the valve sleeve toward or away from the front side of the valve body independent of the rotational movement of the valve sleeve allows the valve sleeve to move away from the housing before it is rotated and then moved back toward the front side of the valve body once the valve sleeve has been rotated, thus forming a tight seal between the sleeve and sealing surface or lip located adjacent the inlet opening provided in the front side of the valve body for admitting dry powder material to the valve. A rubberized layer is added to the exterior surface of the valve sleeve to further enhance the seal between the valve sleeve and the housing. By moving the valve sleeve away from the housing employing the eccentric intermediate sleeve, the layer is disengaged from contact with the housing prior to the valve sleeve being rotated. Otherwise, the layer would be damaged when the valve was opened and closed.
In order to prevent dry powder material from blowing into the mouths of the vacuum breakers, a sleeve shield is provided in the present valve to cover the openings leading to the vacuum breakers. The sleeve shield is sealed to the housing of the valve upstream of the openings that lead to the vacuum breakers, and the sleeve shield extends downstream of the openings.
Finally, the present invention employs ball bearings to suspend the valve sleeve within the housing, thereby making the valve sleeve easier to rotate.